1. Field of the Invention
This invention relates to wireless communications. Specifically, this invention relates to wireless communications with more than one network.
2. Background Information
FIG. 1 shows a model for a wireless communications system that includes an access terminal (AT) 1000, a network for wireless communications (hereinafter ‘wireless network’) 1002, and a service network 1004. The service network 1004 may be a telephone network such as the public switched telephone network (PSTN), a packet-switched data network such as the Internet, or a private network such as a local-area or wide-area network. The wireless network 1002 may be a subscriber network for cellular telephony and/or packet data services. Alternatively, the wireless network 1002 may be a private network (for example, a network that provides wireless connectivity throughout a facility). The AT 1000 may be a mobile unit such as a cellular telephone, a personal digital assistant (PDA) with integrated wireless connection capability, a wireless modem or network card coupled to a laptop computer, or a vehicular access terminal. Alternatively, the AT 1000 may be a fixed unit such as a wireless local loop (WLL) handset or a public access terminal.
A radio access network (RAN) 1006 within the wireless network communicates with the AT 1000 over an air interface. The air interface may include several traffic and control signals, carried over channels that are mutually orthogonal (or nearly orthogonal) in terms of time, frequency, and/or coding. The wireless network 1002 may include several (or many) RANs 1006 placed at physically separate locations such that the geographical service area of the network is extended. In such case, a mechanism may be provided to allow a continuity of communications as the AT 1000 moves between the coverage areas of the RANs 106 (e.g. via a handoff of the air interface from one RAN to another). Each RAN 1006 is coupled to the service network 1004 over one or more channels that may be wired, optical, and/or wireless.
FIG. 2 shows a wireless communications system including a wireless network N10 that communicates with an AT 10 over an air interface A10. Through networks N10 and 40, AT 10 may communicate with a remote server 50. In this example, air interface A10 conforms to Interim Standard IS-856 [e.g. as set forth in “cdma2000 High Rate Packet Data Air Interface Specification”, PN-4875 (TR-45), Telecommunications Industry Association (TIA), Arlington, Va., Sep. 12, 2000]. Such an air interface includes several code-division multiple-access (CDMA) channels for traffic and control signals that are carried over specified uplink and downlink frequency bands.
Wireless network N10 includes a packet data serving node (PDSN) 30 that supports authenticated packet data exchange with a packet-switched data network 40 such as the Internet. Each RAN 20 (also called a radio network node or RNN) may include a base transceiver station (BTS), which terminates the radiolink with the AT, and a base station controller (BSC), which terminates the physical link to PDSN 30 (BTS and BSC not shown). Logical link L10 between a RAN 20 and PDSN 30 is established only as needed to support a session with the AT. In this example, link L10 is a RP link as described in Interim Standard IS-835 [TIA/EIA/IS-835, “Wireless IP Network Standard for cdma2000,” Telecommunications Industry Association, Arlington, Va.].
It may be desirable for a single AT to have the capacity to communicate with more than one service network. For example, it may be desirable for a single AT to have the capacity to provide both wireless voice connectivity with the PSTN and wireless packet data connectivity with the Internet. FIG. 3 shows an example of a wireless communications system in which a dual-use AT 1010 may communicate with two different service networks 1014, 1016 over a single air interface via RAN 1012.
FIG. 4 shows a particular example of a system as shown in FIG. 3, including a wireless network N20 that operates in compliance with Interim Standard IS-2000 [a six-part document defining “cdma2000 spread spectrum systems,” PN-44274432 (TR-45), Telecommunications Industry Association (TIA), Arlington, Va., July, 1999]. AT 15 communicates with network N20 over an air interface A15 that is specified in the IS-2000 standards documents. Through link L20 to mobile switching center 60 (established using a protocol such as Common Channel Signaling System No. 7), a RAN 25 supports voice and SMS (Short Messaging Service) communications between the PSTN 70 and AT 15. Through RP link L30 to PDSN 30, RAN 25 also supports packet data services between a packet-switched data network 40 and AT 15. Communications with AT 15 may be handed off from one RAN 25a to another RAN 25b (e.g. as AT 15 moves between the coverage areas of the RANs), with links L20 and L30 also being handed off as appropriate.
Although air interface A15 provides for packet data services, an IS-2000-compliant network (also called a ‘1×’ network) is optimized to carry voice traffic rather than packet data traffic. An IS-856 network does not support voice traffic, but such a network may be better suited than a 1× network to support the high data rates associated with applications such as wireless Internet connectivity. Although both types of wireless network provide access over air interfaces that include CDMA channels, it is possible to deploy IS-856 and 1× networks to have overlapping areas of coverage (for example, the two air interfaces can be implemented over different frequency allocations) to support optimized delivery of both voice and packet data services throughout a particular geographical area.
Wireless networks that conform to the IS-2000 standard are currently in place, while wireless networks that conform to the IS-856 standard are in advanced stages of development. A need exists to support the reception of communications from one wireless network during an active session with another wireless network in a manner that is compliant with existing standards and/or does not require alterations to infrastructures already in place or about to be deployed.